1. Field of the Invention
The present invention relates to keyboards, and in particular to apparatus for selectively varying the force required to activate the keypad assemblies which make up the keyboard.
2. Description of the Prior Art
Typically the finger-applied force necessary to activate one keypad assembly of a keyboard is the same as the force necessary to activate each of the other keypad assemblies in the keyboard. Users have commonly designated the force necessary to activate the keypad assemblies which make up the array as "touch". Typically "touch" for a keyboard, refers to a single and uniform input force applied to each keypad assembly of the array. However "touch", as defined above, differs greatly from the subjective needs of individual operators, each of whom may require a different "touch" to maximize their efficiency on the same keyboard.
The earliest keyboards were mechanical typewriter keyboards. Users activated individual keys by operating separable mechanical linkages in which a first linkage moved the key against the bias of a spring and successive linkages drove the print head into a ribbon which engaged a paper for imprinting. The spring retained the key in the inactive position. Furthermore, in all mechanical keyboards "touch" was defined only in terms of operator input, but variations in the force applied to the keys by fingers of the operator caused visible differences in the typed output, form word to word, form letter to letter.
Typically electronic keyboards are directed toward replacing certain of the mechanical linkages of early keyboards with electrical and electronic interfaces to thereby transfer from the operator to the keyboard the factor of "touch" thus to minimize the variations in typed output described above. The focus of keyboard improvements today has resided in the production of a uniform typed output, with emphasis on a uniform "touch". For example, U.S. Pat. No. 4,494,109 is directed to varying resistance to movement of the keypad assemblies of the array for the operator's benefit by changing the depth of penetration required to activate a switch to alter "touch". It uses a single circuit to control both keystroke output force and operator "touch".
However, a typewriter keyboard is far different from a multi-function computer keyboard. The computer keyboard provides not only a traditional typewriter keyboard array, but also an array of function keys, a cursor key array, and even a calculator keyset, to serve not only the word processor but also the accountant, the scientist, the engineer. Because different users have different needs, "touch" is best addressed if a direct input can selectively and independently vary the force required to activate the individual keypad assemblies of the array. A multi-function computer keyboard would employ a different "touch" for each separate function of such keyboard, to better enable the user to differentiate between such functions, and additional circuitry would be required for each of the functional key groupings of the keyboard. Alternatively it would be particularly advantageous to be able to selectively and continuously adjust the touch of individual keys so that certain keys, such as the delete or remove key(s), could be given a harder or stiffer touch than the other alpha-numeric keys.